Alkanesulphonic acids and their salts have many industrial uses, which has prompted many producers to seek advantageous processes for production of these compounds. Indeed, the latter find uses as detergents, emulsifiers, and esterification catalysts. These compounds are especially useful for preparation of pharmaceutical products, as hardeners for certain resins, for example aminoalkyd resins and polyurethane resins, and as finishing agents for metals and the like.
Also known are several processes for production of alkanesulphonic acids, for example the oxidation of alkyl mercaptans or of dialkyl sulphides using nitric acid or oxygen, direct sulphonation of alkanes, treatment of alkanes with SO.sub.2 and with oxygen, and action of chlorine on a mercaptan in the presence of water. Each process has its advantages and its shortcomings. The latter have led some industrialists to apply the known reaction of water with an alkanesulphonyl chloride: EQU RSO.sub.2 Cl+H.sub.2 O.fwdarw.RSO.sub.3 H+HCl (1)
which may conveniently be performed with a good yield. See Kirk-Othmer Encyclopaedia, volume 13, pages 350-1954. This process is economically advantageous when an inexpensive source of RSO.sub.2 Cl is available.
Such a hydrolysis process, as applied to methanesulphonyl chloride, is described in Japanese Pat. No. 48-22423 published in 1973. It consists in heating 1 mole of RSO.sub.2 Cl with 1 to 1.5 moles of H.sub.2 O at a temperature of 100.degree. to 140.degree. C. for several hours. This enables the acid RSO.sub.3 H to be obtained with a yield exceeding 99.5%. However, as the reaction product is colored, the Japanese patent recommends that heating should be continued for a few hours, passing a stream of chlorine at the same time. Moreover, the latter may be introduced right from the beginning of the hydrolysis reaction, or alternatively only at the end of this reaction. According to the procedure applied, the preparation lasts on the whole for approximately 2 to 7 hours. Due to the action of chlorine, the product obtained is colorless.
However, in spite of the advantages this Japanese process has over other known techniques, it includes a constraint. This constraint is the use of a chlorine stream, and the subsequent need to drive off the excess of the latter by blowing an inert gas.